PHP page execution time calculation code

<? 
$pagestartime=microtime(); 
?> 
<!--网页内容 start--> 
网页内容 
... 
... 
<!--网页内容 end--> 
<? 
$pageendtime = microtime(); 
$starttime = explode(" ",$pagestartime); 
$endtime = explode(" ",$pageendtime); 
$totaltime = $endtime[0]-$starttime[0]+$endtime[1]-$starttime[1]; 
$timecost = sprintf("%s",$totaltime); 
echo "页面运行时间: $timecost 秒"; 
?>